One known boiling water nuclear reactor includes an RPV positioned in a drywell, or containment, and a passive cooling containment system (PCCS). The RPV contains a core, and the drywell is designed to withstand pressure generated by the RPV and the core during operation. The PCCS is configured to limit the pressure within the containment to a pressure below a design pressure of the containment and to keep the RPV core substantially cool.
A typical PCCS includes a Gravity-Driven Cooling System (GDCS) and a wetwell. The GDCS is substantially isolated from the containment and includes a GDCS pool of water which is coupled to the RPV with an injection line. The wetwell includes a suppression pool of water and is separated from the containment by wall having a spill-over hole therein. The spill-over hole typically is positioned approximately 20 meters above the containment floor, and an equalizing line extends between the suppression pool and the RPV to facilitate transporting water from the suppression pool to the RPV. The equalizing line includes a remotely operated valve which is normally in the closed position and is movable between the closed position and the open position. Particularly, the valve is coupled to a remote computer or workstation, which is configured to transmit signal to the valve to either open or close the valve.
The PCCS further includes a set of passive containment cooling condensers (PCC HXrs) located in a pool of water, or IC/PCC pool, which is positioned outside the containment. The PCC HXrs are configured to condense steam generated within the containment and to drain the condensate to the floor of the containment. Particularly, a steam inlet line extends from within the containment to the PCC HXrs for transporting steam to the PCC HXrs, and a condensate drain line extends from the PCC HXrs and into the containment to transport the condensate, e.g., water, to the containment. The condensate draining from the PCC HXrs accumulates in a lower level of the containment and forms a pool of water.
In operation, the PCCS limits pressure within the containment to a pressure below the design pressure of the containment and keeps the core substantially cool. As one example, if the core begins to decay, e.g., because of a Loss-of-Coolant Accident (LOCA), the decaying core produces heat, which generates steam within the reactor containment. The steam inlet line transports the steam from the containment to the PCC HXrs, which condense the steam into condensate. The condensate is then transmitted from the PCC HXrs back into the containment via the condensate drain line and forms a pool of water in the containment.
After substantial condensation, a surface of the pool of water may reach the spill-over hole and flow through the spill-over hole and into the suppression pool. When condensate flows into the suppression pool, a substantially equal amount of water flows from the suppression pool and into the RPV through the equalizing line. Particularly, the equalizing valve is opened, e.g., by the computer, and water is transported from the suppression pool and into the RPV to keep the core substantially cool.
With the known PCCS, it is necessary for the condensate to form a pool of water almost 20 meters deep before flowing into the suppression pool, and thus causing water to enter the RPV to cool the core. In addition, the PCCS does not include any backup for cooling the core in the event of a possible equalizing line valve malfunction.
It would be desirable to provide an improved PCCS which facilitates cooling the reactor core quicker than with a known PCCS. It also would be desirable to provide such a system which includes a backup system for cooling the reactor core even if the equalizing line valve malfunctions.